1. Field of the Invention
The present invention relates to bleach promoting particles suitable for incorporation into detergent formulations.
2. The Related Art
Hydrogen peroxide releasing compounds have long been known for their capability of removing stains from fabrics. Among the most commonly employed materials for this purpose is sodium perborate, either in the tetrahydrate or monohydrate form.
When laundering fabrics at or near the boil temperatures of 85.degree. to 100.degree. C., perborate and similar persalt materials perform well. Over the years, the temperatures at which consumers launder have however declined. Today it is common to conduct the washing process below 60.degree. C. Under such conditions, the performance of perborate and like materials is poor. To overcome the low temperature problem, hydrogen peroxide releasing agents alternately known as bleach precursors, promoters or activators have been used in conjunction with the persalts.
A recently issued patent, U.S. Pat. No. 4,751,015 (Humphreys et al.) reported an exceptionally effective family of bleach precursor compounds identified as quaternary ammonium or phosphonium substituted carbonic acid esters. A number of problems have been noted with these compounds. Work on the 2-(N,N,N-trimethyl-ammonium)ethyl sodium 4-sulfophenyl carbonate salt (CSPC) has indicated that this compound is very hydrolytically unstable. The hydrolysis rate of CSPC approaches 100%. This rate is measured by placing 7.46 .times. 10.sup.-3 mols/liter of the precursor into a 0.4% w/v detergent solution with continuous stirring at 20.degree. C., in the absence of any peroxy bleach component, under constant pH adjustment to 9.7 for 60 minutes prior to determining the amount of precursor hydrolyzed.
Other precursors have also been described in the literature. For instance, U.S. Pat. No. 4,087,369 (Wevers) reports improving the storage stability of a certain class of perbleach activator (precursor) by agglomeration with an agent that is chemically inert relative to the activator. The class of activators disclosed therein are characterized by a rate of hydrolysis ranging from about 5 to 45% as measured by the aforedescribed hydrolytic stability test procedure. Included among these reasonably stable activators are tetraacetyl ethylene diamine (TAED) and sodium p-benzoyloxybenzene sulfonate (SBOBS). Agglomerating agents suitable for use therein are generically described as having melting points in the range from about 25.degree.-100.degree. C. Specific classes include ethoxylated C.sub.10 -C.sub.18 carboxylic acids, ethoxylated C.sub.10 -C.sub.24 alcohols, C.sub.10 -C.sub.15 amides, polyethylene glycols, ethoxylated C.sub.8 -C.sub.18 alkyl phenols, C.sub.12 -C.sub.30 fatty acids and C.sub.16 -C.sub.30 fatty alcohols.
U.S. Pat. No. 4,009,113 (Green et al.) discloses a slightly different manner of protecting precursor compounds of the type listed by Wevers. Finely divided particulate precursor compound is evenly mixed with an inert carrier material. Around the resultant particle is placed an outer protective, non-deliquescent coherent layer of polyvinyl alcohol, polyacrylamide, starch, water-soluble cellulose ether or water-soluble gum. Among the suitable inert carrier materials are listed lauric acid, sodium dodecyl hydrogen phthalate, sodium dodecyl hydrogen succinate, sodium lauryl sulphate or liquid paraffin.
U.S. Pat. No. 3,925,234 (Hachmann et al.) focuses upon stabilizing bleaching assistants of the N-acyl and O-acyl compound variety. Chief among these compounds is tetraacetyl glycoluril, a material known in the art as having a 60% rate of hydrolysis. Stabilization is accomplished by surrounding the bleaching assistant with an other coating that is a mixture of C.sub.12 -C.sub.24 fatty acid with fatty alcohols (or water-soluble ethoxylated derivatives thereof) in a weight proportion of 10:1 to 2:1.
U.S. Pat. No. 3,833,506 (Fries et al.) is concerned with the same bleaching assistants as those of Hachmann et al. Stabilization is here accomplished by forming an intimate mixture between 10-70% of a bleaching assistant and 30-90% of a mixture of fatty acids and polyethylene glycol.
U.S. Pat. No. 4,678,594 (Parfomak et al.) encapsulates a mixture of sodium nonanoyloxybenzene sulfonate (SNOBS) and sodium perborate in a matrix of nonionic ethoxylated alcohol surfactant. Use of ethoxylated nonionic surfactant as a storage stability and water-dispersibility aid for peroxy acid bleach precursors is also reported in U.S. Pat. No. 4,399,049 (Gray et al.).
U.S. Pat. No. 4,486,327 (Murphy et al.) focuses upon branched alpha-substituted derivatives of C.sub.6 -C.sub.18 carboxylic acid ester type activators. Better storage stability of the activator is achieved by evenly distributing therewith a binder material which may be selected from nonionic surfactants, polyethylene glycols, anionic surfactants, film-forming polymers, fatty acids and mixtures thereof.
Other patents directed toward solving storage stability and/or dispersibility problems for bleach precursors include U.S. Pat. No. 4,444,674 (Gray), U.S. Pat. No. 4,111,826 (Leigh et al.), and U.S. Pat. No. 4,372,868 (Saran et al.).
None of the aforementioned art has focused upon solving the substantially greater hydrolytic instability problem presented by the quaternary ammonium carbonic acid precursors, such as CSPC, described by Humphreys et al. These compounds have unique chemical breakdown products and mechanisms that necessitate unique solutions. Not only must the proper stabilization agent be provided but dispersibility in the wash liquor must not thereby be hindered.
Accordingly, it is an object of the present invention to provide bleach precursor particles that have improved hydrolytic stability and thereby prolonged storage capability.
It is another object of the present invention to provide bleach precursor particles that are not only storage stable but also exhibit excellent water dispersibility in a wash medium.
A still further object of the present invention is to provide a detergent composition containing the bleach activator particle which will deliver a high level of bleach performance against stains.
These and other objects of the invention will become more apparent through the detailed description provided below.